Koi
Cyprinus carpio
The Koi (Cyprinus carpio) is a peaceful fish that's rewarding to keep. Give it a tank of at least 3000 litres (793 US gallons), water held at 39-82°F, and a pH of 6.5-8.5. Always keep a group of at least 3 - they feel safest in numbers.
Captive lifespan reflects typical experience in a home aquarium, not maximum recorded age; genetics, sourcing, and care vary.
Natural distribution
Asia (ornamental domesticated Common Carp)
- East & Southeast Asia
Regional colours match the stocking calculator's origin map.
Koi Tank Setup
A tank of at least 3000 litres (793 US gallons) works well. Keep the water at 39-82°F with a pH around 6.5-8.5, and set up both cover and open swimming space where they spend most of their time (Mid). Always keep a group of at least 3 of their own kind - kept alone or in pairs they tend to turn shy, nippy, or wash out in colour. They grow to around 90 cm, so plan the tank size and filtration for a full-grown adult rather than the small juvenile you see in the shop.
What Do Kois Eat?
They're not fussy eaters - feed a varied diet, rotating good-quality dry, frozen, and gel foods rather than the same thing every day, and match the food size to their mouths.
Koi Tank Mates
NOT SUITABLE FOR STANDARD AQUARIUMS. Koi routinely grow 45-90cm and can live 25+ years; they need an outdoor pond of several thousand litres with heavy-duty filtration, not an indoor tank. Extremely high bioload - one adult koi produces as much waste as dozens of tropical fish. If keeping indoors as juveniles, plan the pond upgrade well before they outgrow a tank. The Koi is peaceful, which is the first thing to weigh up when you choose tank mates. At around 90 cm fully grown, it needs tank mates that can hold their own against its size and appetite. It's a shoaling fish, so settle a group of 3 or more of its own kind before adding anything else - a stressed, lonely fish is far more likely to nip or hide. Before you buy, run your full stocking list through our stocking calculator. It weighs temperament, adult size, and water needs together, which a single species page can't do on its own.
Are Kois Good for Beginners?
Not a sensible first purchase. Get the tank cycled, keep easier fish stable for a year, then revisit if you still want the extra work this species demands.
Koi - frequently asked questions
What size tank do Kois need?
Kois need a tank of at least 3000 litres (793 US gallons). A bigger tank is always easier to keep stable, and gives them more room to settle in and behave naturally.
How many Kois should I keep together?
Keep a group of at least 3. Kois are a shoaling species and become stressed, lose their colour, or hide when kept singly or in pairs.
What water parameters do Kois need?
Keep them at 39-82°F with a pH of 6.5-8.5, steady rather than chased to an exact figure. In a cycled tank, ammonia and nitrite should both read 0 ppm, with nitrate kept low through regular water changes.
What do Kois eat?
Kois are omnivores and aren't fussy eaters. Feed a varied mix of good-quality dry, frozen, and gel foods, and match the food size to their mouths. Feed small amounts once or twice a day, and remove anything they don't eat.
Are Kois good for beginners?
It depends on the setup. Match Kois to how often you actually test water and perform maintenance.
Common mistakes with Kois
- Underestimating tank size - the minimum footprint is 3000 litres (793 US gallons); impulse buying into a smaller tank leads to stress and shortened lifespan.
Building a community? Run the full list through the stocking calculator before you add anything else.
Great tank mates
Chosen from temperament, overlapping temperature/pH bands, plausible minimum tank footprints, and size versus yours in App-aquatic data. Hobby nuance always wins - verify stocking and temperament before purchasing.
Check Koi against any other fish → Compares water parameters, predation risk, fin nipping and tank size, and draws both at life size.
Fish to avoid mixing with Kois
These well-known species are commonly sold alongside this fish but are not recommended tank mates - verify before purchasing.
- OscarPredator - Oscar will eat or injure smaller tank mates
- AxolotlPredator - Axolotl will eat or injure smaller tank mates
- Common GoldfishGoldfish - prefer cooler, harder water that tropical fish cannot tolerate
